Foundation pilings are used to support and stabilize structures, such as large and/or tall buildings, that cannot be adequately supported by the soil under the structure alone. Prior art friction pilings, which do not rest on a solid base such as rock, are understood to have a compressive capacity generally proportional to their length. Tension produced in soil surrounding the piling increases as soil is displaced during placement causing greater friction against the sides of the pilings. Pilings are usually made of timber, concrete or steel. Timber is the longest-used piling choice, being a natural, accessible, renewable resource. As other materials have developed, the choice has come to depend upon several factors including the environment where the pile will be placed.
Foundation pilings are particularly critical for structures built in areas known to have soft soils like oceanfront lots in coastal regions. Coastal regions have recently seen an increase in popularity and population and, as a result, construction of homes and other buildings. Soil near the coast has a higher water content and are less solid than inland areas, which are more solid and often have rock underneath the soils into which foundation pilings can be embedded. As a result, foundation pilings can support heavier loads in inland areas than in coastal areas.
Some coastal areas are also known to be prone to seismic activity, namely, earthquakes and tremors. Seismic activity presents another concern for construction since buildings are exposed to lateral tension, or sway left and right, during seismic activity. In areas having soft soils and seismic activity, foundation pilings provide adequate support for structures and making them better able to withstand small tremors or higher seismic activity in the soils.
There are several well-known methods for putting foundation pilings into place for construction. One widely-used method is to insert a piling column into a hole and then drive it down into the soil by pounding it with equipment fitted with a hydraulic ram, known as a pile driver. Driving piles requires prefabricated piles, which may be very long and heavy and require large, heavy equipment to transport the piles and to pound, i.e., drive, them into place, and the pounding creates considerable vibration and noise and is slow-going. Sometimes certain types of pilings cannot be pounded due to conditions of the soil at the site. Or, the choice of piling material will be dictated by the composition of the structure being constructed on the piles.
Another method for placing pilings, and alternative to driving, uses a helical screw mounted at the end of a shaft that can be screwed downward into soil until the screw is seated in a region of soil that sufficiently strong to support the weight that will be placed on the shaft. These are commonly referred to as “helical pier systems,” one well-known example being the CHANCE helical pier system available from the A.B. Chance Company of Centralia, Mo., USA. Vickars, et al., U.S. Pat. No. 5,707,180 discloses a screw pier that is drawn downwardly into soil and attached to a shaft, typically having a square shape, that carries soil displacement means. Turning of the screw and shaft draws the soil displacement means through the soil forcing the soil out of a region around the shaft to create an opening that is then filled with grout that once solidified, encases the shaft and creates a column that becomes the foundation piling.
Addition of solidified grout increases the diameter of the piling beyond that of prior art pilings, which consisted of just the shaft placed in the soil. The significantly larger diameter of the solidified grout column is able to withstand more force before becoming displaced in comparison to a prior art helical pier in the same soil. As such, the solidified grout column has a significantly increased capacity for bearing compressive loads when compared to a prior art helical pier consisting only of a similarly-sized shaft and screw without grout.
In addition, “stepped pilings” are pilings that increase stepwise in diameter along their length and generally have greater load bearing capacities than pilings having a constant diameter. U.S. Pat. No. 6,652,195, also to Vickars, et al., discloses a method for making a “stepped pile” using a plurality of soil displacing members increasing in size spaced along the shaft attached to the screw pier, such that the opening created around the shaft is smallest nearest the screw pier and gradually becomes larger toward the end of the shaft nearest to the earth's surface.
Helical pier systems have been used for many years. These systems do not require pre-manufacture of large columns that are complicated to move or large equipment for placement of the pilings since the pilings are made at the site in the position where they are needed to provide support.
Construction demands in areas having soft soils and in areas where driven pilings cannot be used for some reason have created a need for a method to make foundation pilings that can withstand greater loads than the methods and pilings that are currently accepted and used. There is a need, whatever method is selected, for lessening the amount of time required to construct and place foundation pilings for construction projects because saving time saves money.